Olympiakos have a five-point lead over Panathinaikos at the halfway point in the Super League after beating last-placed Larissa on Sunday.
The Reds now have a clear advantage over their rivals, who will be stewing as the Greek championship goes into its winter break. The next round of games will be on January 4 and 5.
Olympiakos took the lead at AEL Arena in the 36th minute through a Panagiotis Katsiaros own goal. The defender deflected a shot from Olof Mellberg past his keeper.
In his first game in charge of the Thessaly club, former Mainz coach Jorn Andersen was not able to spur the home side on to an equaliser although they felt they should have had a second-half penalty.
The freezing conditions at one point led to play being held up as Larissa fans were asked to stop throwing snowballs onto the pitch.
Olympiakos, however, held on to win the game and go into the two-week break as so-called “winter champions” but more importantly with a lead over Panathinaikos that they can build on after the Greens slumped to a home defeat to Olympiakos Volou on Saturday.
None of the chasing pack were able to make up ground on Panathinaikos as PAOK, AEK and Aris slumped to surprise defeats on Sunday.
AEK were beaten 2-0 by Iraklis in Thessaloniki. Desperate for three points after a series of defeats and draws, Iraklis got a great start when Ricardo Dani gave them the lead after poking home a loose ball following a corner a few minutes before half time.
Manolis Papasterioanos made it 2-0 on 58 minutes with a swerving shot from outside the area and Iraklis, who have also beaten Olympiakos and Aris at home, held on to make it a disappointing week for AEK who also went out of the Europa League.
The win moves Iraklis up to 10th place on 19 points, just four behind AEK in fourth.
PAOK are also on 23 points after being beaten 2-1 at Kerkyra. The home side took the lead after just six minutes through a first-time volley from the edge of the area from Ilias Ioannou.
PAOK managed to equalise on the stroke of half time with Stefanos Athanasiadis, who volleyed home an Adelino Vierinha cross.
But former Olympiakos midfielder Ieroklis Stoltidis got the winning goal in the 50th minute, bundling home a deflected shot.
Aris slipped to seventh on 20 points and were leapfrogged by Xanthi who went joint-fifth with Kavala on 21 points after coming away from Thessaloniki with a 2-0 win.
Dimitris Souanis gave rapidly-improving Xanthi the lead on 22 minutes after outpacing the Yellows’ defense and finishing with a low shot.
The home side’s hopes of getting back into the game received a major blow on 35 minutes when Kristi Vangeli was sent off after receiving two yellow cards following an altercation with Marcelinho.
The visitors took full advantage, with Souanis grabbing his second on 62 minutes after Michalis Sifakis failed to hold his header.